Biochemical Characterization of QPX7728, a New Ultra-Broad-Spectrum Beta-lactamase Inhibitor of Serine and Metallo-Beta-Lactamases.

QPX7728 is a new ultra-broad-spectrum inhibitor of serine and metallo beta-lactamases from a class of cyclic boronates that gave rise to vaborbactam. The spectrum and mechanism of beta-lactamase inhibition by QPX7728 were assessed using purified enzymes from all molecular classes. QPX7728 inhibits class A ESBLs (IC50 range 1-3 nM) and carbapenemases such as KPC (IC50 2.9+/-0.4 nM) as well as class C P99 (IC50 of 22+/-8 nM) with a potency that is comparable or higher than recently FDA approved BLIs avibactam, relebactam and vaborbactam. Unlike those other BLIs, QPX7728 is also a potent inhibitor of class D carbapenemases such as OXA-48 from Enterobacteriaceae and OXA enzymes from A. baumannii (OXA-23/24/58, IC50 range 1-2 nM) as well as MBLs such as NDM-1 (IC50 55+/-25 nM), VIM-1 (IC50 14+/-4 nM) and IMP-1 (IC50 610+/-70 nM). Inhibition of serine enzymes by QPX7728 is associated with progressive inactivation with a high efficiency k 2/K ranging from of 6.3 x 10(4) (for P99) to 9.9 x 10(5) M(-1) s(-1) (for OXA-23). This inhibition is reversible with variable stability of the QPX7728-beta-lactamase complexes with target residence time ranging from minutes to several hours: 5-20 minutes for OXA carbapenemases from A. baumanii, approximately 50 minutes for OXA-48 and 2-3 hours for KPC and CTX-M-15. QPX7728 inhibited all tested serine enzymes at 1:1 molar ratio. Metallo-beta-lactamases NDM, VIM, and IMP were inhibited by a competitive mechanism with fast-on-fast-off kinetics, with Kis of 7.5+/-2.1 nM, 32+/-14 nM and 240+/-30 nM for VIM-1, NDM-1 and IMP-1, respectively. QPX7728 ultra-broad-spectrum of BLI inhibition combined with its high potency enables combinations with multiple different beta-lactam antibiotics.